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Galerucella calmariensis and G. pusilla
(Coleoptera: Chrysomelidae)
These native European beetles were introduced to North America in 1992 as part of a 5-15 year program
to control purple loosestrife, an exotic weed infesting North American wetlands. Release sites were New
York, Pennsylvania, Maryland, Virginia, Minnesota, Oregon, and Washington state in the United States,
and sites in Canada. Since 1992, releases have been made in Ohio, Indiana, Illinois, Iowa, Michigan,
Wisconsin, South Dakota, Colorado and Montana. Colonization of these introduced populations appears
to have been successful.
Appearance
G. calmariensis: Light brown, usually with a black triangle or a broad, dark stripe on the thorax. The body
has parallel sides, is 3-5 mm long and half as wide, and is punctuated with coarse dots and fine, dense
hairs.
G. pusilla: Light brown, usually with a narrow dark stripe on the thorax. The body has fine, dense hairs,
parallel sides, is 3-4 mm long and about half as wide, with a slight narrowing toward the head. G. pusilla is
also punctate, but less coarsely so than G. calmariensis.
Habitat
Purple loosestrife is a weed species in wetlands over much of temperate North America, and the aim of
the introduction program of G. calmariensis and G. pusilla is to locate the releases so that these beetles
will be able to easily colonize and spread. Currently, purple loosestrife exists in monotypic stands
throughout the northeastern U.S. and southeastern Canada, the Midwestern U.S., and in isolated locales
in the western U.S. and southwestern Canada. Irrigation systems provide conduits for its spread in dry
areas.
Pests Attacked
G. calmariensis and G. pusilla are considered host-specific to purple loosestrife (Lythrum salicaria).
Before introduction to North America, approximately 50 native plants, including some close relatives of
purple loosestrife, were tested for susceptibility to these beetles. Only winged loosestrife (Lythrum alatum)
was a potential host, and under field conditions in Europe, it was determined that if given a choice, G.
calmariensis and G. pusilla avoided the North American native.
Life Cycle
G. calmariensis and G. pusilla have very similar life habits. Adults emerge in spring from hibernation in
leaf litter and feed on the new leaves and shoots of purple loosestrife. The egg laying phase lasts
approximately two months in the spring and eggs are laid in clusters of two to ten daily on the plant stem
and in the leaf axils. A female can lay 300-400 eggs per year, and the adult lives 8-10 weeks. Larvae feed
on bud, leaf, and stem tissue. Pupation takes place in the soil or ground cover near the plants. From egg
to adult takes about 6 weeks, and there is generally one generation per year.
Adults are very mobile and successful in seeking out new stands of purple loosestrife. Most searching for
a host plant occurs after hibernation when plant growth is at a peak, and again following the emergence of
new beetles in July and August. Once a host has been located, migration slows. The overwintered adults
die by late June, soon after the reproduction phase has been completed.
Relative Effectiveness
In Europe, there are several insects which act together to control purple loosestrife. As a result, only
small, scattered stands of the plant exist. The current program includes the introduction of these
Galerucella spp., the weevil Hylobius transversovittatus and the planned release of two flower-eating
species which are also specific to purple loosestrife. It is predicted that upon establishment of these
species, North American purple loosestrife will be reduced by 90% over approximately 90% of its present
range.
Plants growing in high water and in shade are not hospitable sites for Galerucella.
Top: A large stand of purple loosestrife.
Photo: R.A.Malecki
Center: Galerucella adult.
Photo: B.Blossey
Pesticide Susceptibility
Early indications are that the Galerucella spp are very susceptible to pesticides; exposure should be
strictly avoided. Conservation sites where purple loosestrife is continuously distributed and which are free
of standing water most of the year are optimal. To establish a colony of Galerucella will probably take 7-10
years and the site (5-10 acres is adequate) should be safe from land development and broad spectrum
insecticides during that time.
Commercial Availability
Not available commercially at this time.
Acknowledgments
Thanks to Richard Malecki and Bernd Blossey for providing information and photographs and to Richard
Malecki for reviewing this section.
References
Blossey, B., Schroeder, D., Hight, S.D., and Malecki, R.A. (1994) Host specificity and environmental
impact of two leaf beetles (Galerucella calmariensis and G. pusilla) for biological control of purple
loosestrife (Lythrum salicaria). Weed Sci., 42: 134-140.
Kok, L.T., McAvoy, T.J., Malecki, R.A., Hight, S.D., Drea, J.J., and Coulson, J.R. (1992) Host specificity
tests of Galerucella calmariensis (L.) and G. pusilla(Duft.) (Coleoptera: Chrysomelidae), potential
biological control agents of purple loosestrife, Lythrum salicaria L. (Lythraceae), Bio. Control, 2: 282-290.
Malecki, R.A., Blossey, B., Hight, S.D., Schroeder, D., Kok, L.T., and Coulson, J.R. (1993) Biological
control of purple loosestrife: a case for using insects as control agents, after rigorous screening, and for
integrating release strategies with research. BioSci., 43: 680-686.
Manguin, S., White, R., Blossey, B., and Hight, S.D. (1993) Genetics, taxonomy, and ecology of certain
species of Galerucella (Coleoptera: Chrysomelidae). Ann. Entomol. Soc. Am., 86: 397-410.
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Bottom: Leaf damage caused by
Galerucella.
Photo: B.Blossey
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